This invention relates to the transportation of fuel elements which have been irradiated in a nuclear reactor. In the present context a nuclear reactor fuel element is to be understood to include not only the type of element whose content of fissile material is such that under irradiation in the reactor the primary purpose is the generation of power brought about by fission but also the type of element which is commonly known as a breeder element, one whose content of fertile material is such that under irradiation in the reactor the primary purpose is the conversion of fertile material into fissile material.
Transportation is necessary for the conveyance of the fuel element from the nuclear reactor in which it has been irradiated to a reprocessing or storage facility, the usual objective being to subject the element after appropriate storage and dismantling steps to a reprocessing operation by which certain re-usable components, particularly fissile components, are recovered. Subsequent to irradiation the fuel element is not only radioactive but also continues to generate heat on account of the radioactive decay of fission products. The requirement for safe transportation therefore calls for comprehensive and expensive equipment.
It is generally the case at the present time that an irradiated fuel transport container consists basically of two main parts, a flask on the one hand and an inner container or bottle on the other hand, the latter being designed to be accommodated inside the flask in company with such other means as may be necessary to complete the shielding and cooling functions of the unit. Taking for granted that several fuel elements are to be carried simultaneously in the transport container, an important purpose of the inner container is to maintain the relative positioning of the elements inside the flask which constitutes an outer envelope. The term "bottle" applied to the inner container connotes a containing structure which is fully sealable, a feature which is especially desirable if there is any liklihood that the fuel elements to be transported will leak or otherwise give rise to a release of fission products into the immediate surroundings. The bottle then constitutes an inner, second envelope but except where specified to the contrary no limitation as to sealability is to be inferred from the references made herein to "inner container".
The transport container as a whole must cater not only for safety in transit but also for safe loading and unloading. As regards unloading, the usual practice is to submerge the complete container in a pond of water and to undertake the opening of the container and the withdrawal of the fuel elements under submerged conditions. The purpose of the pond in this connection is mainly to afford transparent shielding for the operatives, a purpose which would be frustrated if the pond were to become heavily contaminated. Bearing in mind that fuel elements discharged from a nuclear reactor may carry adherent extraneous solid matter, an example of which is the so-called "crud" occurring in reactors cooled by water, steps are desirable for ensuring the removal of such solid matter before exposure of the fuel elements to the pond water. To this end the medium in which the elements have travelled, usually water or possibly some other liquid, is removed in separation from the pond water and with this removed liquid may be entrained some of the solid matter. For completing removal of the solid matter a flushing liquid may be introduced and one of the objects of the invention is to facilitate reliable and expeditious performance of the flushing operation.